fix bug about reload knowledgebase configuration reloading (#210)

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

Issue link:#[[Link the issue
here](https://github.com/infiniflow/ragflow/issues/209)]

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/app/qa.py

@@ -133,7 +133,7 @@ def chunk(filename, binary=None, lang="Chinese", callback=None, **kwargs):
         return res
 
     raise NotImplementedError(
-        "file type not supported yet(pptx, pdf supported)")
+        "Excel and csv(txt) format files are supported.")
 
 
 if __name__ == "__main__":